The present invention relates to a water-degradable or flushable polyolefin-containing film. More particularly, the present invention relates to a water-degradable or flushable polyolefin-containing film having greater than about 55 weight percent of a modified polyolefin and less than about 45 weight percent of poly(ethylene oxide).
Such articles typically have some portion, usually the backing layer, liner, or baffle constructed of a liquid repellent film material. This repellent material is appropriately constructed to minimize or prevent the exudation of the absorbed liquid from the article and to obtain greater utilization of the absorbent capacity of the product. The liquid repellent film commonly used includes plastic materials such as polyethylene films and the like.
Although such products are relatively inexpensive, sanitary and easy to use, disposal of a soiled product is not without its problems. With greater interest being placed in protecting the environment today, there is a need to develop materials that are more compatible with the existing and developing waste disposal technologies while still delivering performance consumers have come to expect. An ideal disposal alternative would be to use municipal sewage treatment and private residential septic systems. Products suited for disposal in sewage systems can be flushed down a convenient toilet and are termed xe2x80x9cflushable.xe2x80x9d While flushing such articles would be convenient, the liquid repellent material which normally does not disintegrate in water tends to plug toilets and sewer pipes. It therefore becomes necessary, although undesirable, to separate the barrier film material from the absorbent article prior to flushing.
In addition to the article itself, typically the packaging in which the disposable article is distributed is also made from a water resistant material. Water resistivity is necessary to prevent the degradation of the packaging from environmental conditions and to protect the disposable articles therein. Although this packaging may be safely stored with other refuse for commercial disposal, and especially in the case of individual packaging of the products, it is often more convenient to dispose of the packaging in the toilet with the discarded disposable article. However, in the cases where such packaging is composed of a water resistant material, plugging of the drains to the toilet typically results.
Desirably, a commercial, flushable product should be relatively responsive to water and be transportable in a sewer system. Commercially available water-soluble polymers, such as polyethylene oxide (PEO), polyvinyl alcohol (PVOH), acrylamide polymers, acrylic acid-based polymers, and cellulose derivatives, possess the desired characteristics for flushability, such as water solubility and/or water dispersibility. However, due to their in-use degradability and storage degradation, these materials function poorly as components in personal care products. Other disadvantages are that these polymers are difficult to process and are substantially more expensive than polyolefins.
The requirements for a functional and flushable product provide a substantial challenge in finding suitable materials with the desired properties. In an attempt to overcome the flushability problem of a water resistant film the prior art has modified the water resistant polymer. One of the more useful ways of modifying polymers involves blending them with other polymers of different structures and properties.
Polymer blends of polyolefins and poly(ethylene oxide) have been shown to be water modifiable at expectedly low weight % polyolefin levels. Such blends would be anticipated to be flushable when exposed to water in a toilet but do not possess the dry mechanical properties required for functionality in use. Moreover, the high content of poly(ethylene oxide) makes such materials prohibitively expensive for use in a disposable personal hygiene article such as a sanitary napkin, diaper and the like. Polymer blends of polyolefins and poly(ethylene oxide) containing greater than about weight percent of polyolefin are generally water resistant and are not water modifiable.
In view of the problems of the prior art, it remains highly desirable to provide a water modifiable film having a substantial portion of thereof composed of a polyolefin. More desirably, the water modifiable film should have greater than about 55 weight percent of a polyolefin. When dry, the film should have the mechanical properties necessary for functionality. When wet, the films should lose at least a portion of its mechanical properties which would render the film flushable and transportable in a sewer system. Such films could be used for making flushable barrier films for personal care products.
It is therefore an object of the invention to provide a polyolefin-containing film that is water modifiable or water-degradable which contains higher levels of polyolefin content. More specifically, it is an object of the invention to provide a polyolefin-containing film having greater than about 55 weight percent of a polyolefin and less than about 45 weight percent of poly(ethylene oxide) that is water-modifiable or water degradable.
In its principal embodiment, the present invention provides a water-modifiable or water-degradable film comprising at least about 55 weight percent of a modified polyolefin and no more than about 45 weight percent of poly(ethylene oxide). The polyolefin is modified by having from about 0.1 weight percent to about 30 weight percent, based on the total weight of the polyolefin and poly(ethylene oxide), of a monomer grafted onto the polyolefin backbone. Preferably the monomer is 2-hydroxyethyl methacrylate or polyethylene glycol ethyl ether methacrylate. The film of the invention has a loss of at least 10% in two or more tensile properties selected from percent strain-to-break, peak stress, energy-to-break and modulus after being immersed in water for 30 seconds.
In an alternative embodiment, the present invention provides a flushable personal care article having a backing or barrier layer comprising a water-modifiable or water-degradable film comprising greater than about 55 weight percent of a modified polyolefin and less than about 45 weight percent of poly(ethylene oxide). The polyolefin is modified by having from about 0.1 weight percent to about 30 weight percent, based on the total weight of the polyolefin and poly(ethylene oxide), of a monomer grafted onto the polyolefin backbone. Preferably the monomer is 2-hydroxy-ethyl methacrylate or polyethylene glycol ethyl ether methacrylate. The film comprising the backing or barrier layer of the invention has a loss of at least 10% in two or more tensile properties selected from percent strain-to-break, peak stress, energy-to-break and modulus after being immersed in water for 30 seconds.
As used herein xe2x80x9cwater modifiablexe2x80x9d means that a four mil thick film (one mil equals 0.001 of an inch or 0.025 mm), when immersed in water for 30 seconds, will have modified by greater than 10% two or more of the following tensile properties: percent strain-to-break, peak stress, energy-to-break and modulus. To determine the degree of modification, the xe2x80x9cwetxe2x80x9d values are compared to the pre-immersed or xe2x80x9cdryxe2x80x9d film values.
The term xe2x80x9cpersonal care productxe2x80x9d or xe2x80x9cpersonal care articlexe2x80x9d means articles such as infant diapers, sanitary napkins, adult incontinence garments, and the like.
By the term xe2x80x9cbacking layerxe2x80x9d or xe2x80x9cbarrier layerxe2x80x9d is meant that component of an infant diaper, sanitary napkin, adult incontinence garment or the like which is worn during normal use furthest from the user""s body and which serves to minimize or prevent the exudation of the absorbed liquid.
Although the present invention is described with reference to a water modifiable film and, in particular, to personal care articles having a backing layer, liner, or barrier layer comprising such films, one skilled in the art will understand that the composition of the invention can be used to make other thermoplastic articles that can be extruded or injection molded in which the desired property of water degradability is needed such as packaging articles and the like.
The saturated ethylene polymers useful in the practice of this invention are homopolymers or copolymers of ethylene and polypropylene and are essentially linear in structure. As used herein, the term xe2x80x9csaturatedxe2x80x9d refers to polymers which are fully saturated, but also includes polymers containing up to about 5% unsaturation. The homopolymers of ethylene include those prepared under either low pressure, i.e., linear low density or high density polyethylene, or high pressure, i.e., branched or low density polyethylene. The high density polyethylenes are generally characterized by a density that is about equal to or greater than 0.94 grams per cubic centimeter (g/cc). Generally, the high density polyethylenes useful as the base resin in the present invention have a density ranging from about 0.94 g/cc to about 0.97 g/cc. The polyethylenes can have a melt index, as measured at 2.16 kg and 190xc2x0 C., ranging from about 0.005 decigrams per minute (dg/min) to 100 dg/min. Desirably, the polyethylene has a melt index of 0.01 dg/min to about 50 dg/min and more desirably of 0.05 dg/min to about 25 dg/min.
Alternatively, mixtures of various grades of polyethylene can be used as the base resin in producing the graft copolymer compositions, and such mixtures can have a melt index greater than 0.005 dg/min to less than about 100 dg/min.
The low density polyethylene has a density of less than 0.94 g/cc and are usually in the range of 0.91 g/cc to about 0.93 g/cc. The low density polyethylene has a melt index ranging from about 0.05 dg/min to about 100 dg/min and desirably from 0.05 dg/min to about 20 dg/min. Ultra low density polyethylene can be used in accordance with the present invention. Generally, ultra low density polyethylene has a density of less than 0.90 g/cc.
Generally, polypropylene has a semi-crystalline structure having a weight average molecular weight of about 40,000 or more, a density of about 0.90 g/cc, a melting point of 168 to 171xc2x0 C. for isotactic polypropylene and a tensile strength of 5000 psi. Polypropylene can also have other tacticities including syndiotactic and atactic.
The above polyolefins can also be manufactured by using the well known multiple-site Ziegler-Natta catalysts or the more recent single-site metallocene catalysts. The metallocene catalyzed polyolefins have better controlled polymer microstructures than polyolefins manufactured using Ziegler-Natta catalysts, including narrower molecular weight distribution, well controlled chemical composition distribution, co-monomer sequence length distribution, and stereoregularity. Metallocene catalysts are known to polymerize propylene into atactic, isotactic, syndiotactic, isotactic-atactic stereoblock copolymer.
Copolymers of ethylene which can be useful in the present invention may include copolymers of ethylene with one or more additional polymerizable, unsaturated monomers. Examples of such copolymers include, but are not limited to, copolymers of ethylene and alpha olefins (such as propylene, butene, hexene or octene) including linear low density polyethylene, copolymers of ethylene and vinyl esters of linear or branched carboxylic acids having 1-24 carbon atoms such as ethylene-vinyl acetate copolymers, and copolymers of ethylene and acrylic or methacrylic esters of linear, branched or cyclic alkanols having 1-28 carbon atoms. Examples of these latter copolymers include ethylene-alkyl (meth)acrylate copolymers, such as ethylene-methyl acrylate copolymers.
Poly(ethylene oxide) polymers suitable for use in the films of the invention are available from Union Carbide Corporation, Danbury, Conn. under the trade name of POLYOX(copyright). Typically, poly(ethylene oxide) is a dry free flowing white powder having a crystalline melting point in the order of about 65xc2x0 C., above which poly(ethylene oxide) resin becomes thermoplastic and can be formed by molding, extrusion and other methods known in the art.
In the principal embodiment of the invention, the water-modifiable film comprises at least about 55 weight percent of a modified polyolefin and no more than about 45 weight percent of unmodified poly(ethylene oxide). Desirably, the water modifiable film comprises from about 55 weight percent to about 85 weight percent of a modified polyolefin and from about 45 weight percent to about 15 weight percent of unmodified poly(ethylene oxide). More desirably, the water-modifiable film comprises from about 65 weight percent to about 85 weight percent of a modified polyolefin and from about 35 weight percent to about 15 weight percent of unmodified poly(ethylene oxide).
The polyolefin is modified by having grafted thereto from about 0.1 weight percent to about 30 weight percent, based on the weight of the polyolefin and poly(ethylene oxide), of a monomer. Desirably, the polyolefin is modified by having grafted thereto from about 1 weight percent to about 20 weight percent, and more desirably, from about 1 weight percent to about 10 weight percent, based on the weight of the polyolefin and poly(ethylene oxide), of a monomer. Preferred and thus exemplary monomers for graft-polymerization modification of the polyolefins include 2-hydroxyethyl methacrylate or polyethylene glycol ethyl ether methacrylate.
Generally, the modified polyolefin is made by feeding to an extruder an amount of polyolefin, monomer and a free radical initiator. The modified polyolefin and poly(ethylene oxide) is then melt blended in an extruder to form the water modifiable film. The method of making the modified polyolefin is described in greater detail in copending U.S. patent application 08/733,410 filed Oct. 18, 1996 entitled xe2x80x9cMethod of Making Polyolefins Having Greater Than 5 Percent 2-Hydroxyethyl Methacrylate Grafted Theretoxe2x80x9d, the entire disclosure of which is incorporated herein by reference. In accordance with this embodiment of the invention, suitable poly(ethylene oxide) polymers can have an average molecular weight ranging from 100,000 to about 8,000,000 gm/mole.
The free radical initiators which can be used to graft the monomer onto the polyolefin include acyl peroxides such as benzoyl peroxide; dialkyl; diaryl; or aralkyl peroxides such as di-t-butyl peroxide; dicumyl peroxide; cumyl butyl peroxide; 1,1-di-t-butyl peroxy-3,5,5-trimethylcyclohexane; 2,5-dimethyl-2,5-di(t-butylperoxy) hexane; 2,5-dimethyl-2,5bis-(t-butylperoxy)hexyne-3 and bis-(p-t-butyl peroxyisopropylbenzene); peroxyesters such as t-butyl peroxypivalate; t-butyl peroctoate; t-butyl perbenzoate; 2,5-dimethylhexyl-2,5-di(perbenzoate); t-butyl di-(per phthalate); dialkyl peroxymonocarbonates and peroxydicarbonates; hydroperoxides such as t-butyl hydroperoxide, p-menthane hydroperoxide, pinane hydroperoxide and cumene hydroperoxide and ketone peroxides such as cyclohexanone peroxide and methyl ethyl ketone peroxide. Azo compounds such as azo-bis-isobutyronitrile may also be used.
When modifying the polyolefin, the amount of free radical initiator added to the extruder should be an amount sufficient to graft from about 1 percent to 100 percent of the monomer onto the polymer, i.e., the polyolefin. This can range from about 0.1 weight percent to about 2 weight percent of initiator. Preferably, the amount of initiator added to the extruder ranges from about 0.1 weight percent to about 1 weight percent wherein all such ranges are based on the amount of monomer added to the melt blend.
The water-modifiable modified polyolefin-containing films of the present invention will, when immersed in water for about 30 seconds, have modified at least two of the tensile properties: percent stain-to-break, peak stress, energy-to-break and modulus by greater than 10%. Desirably, at least two of the tensile properties will be reduced greater than about 25%. More desirably, at least two of the tensile properties will be reduced from about 25% to about 98%, and even more desirably at least two of the tensile properties: percent stain-to-break, peak stress, energy-to-break and modulus will be reduced from about 30% to about 80%. The values in determining the extent of the tensile property or properties modification are relative to the dry condition, i.e. pre-immersion value for that measured property.